Two stroke engine help

Hey Ns, I just recently bought a yz250 ts and the bitch does not start. The only way I can get it to start is by taking the sparkplug off and spraying starter fluid into the cylinder. Once it's running it runs great but it just won't start if I dont do that. It has good spark, and good compression. I ordered a new main jet and pilot jet because I read that would help to go a bit smaller, any ideas from you?

If the FAR is fucked then you should fix that before you cook/drown another plug. If it has spark and compression and it's getting fuel then your FAR is likely off and your carbs are derping. Is the plug soaked in gas or dry? Clean it off and try to start it, see if gas is even getting to it.

apttPretty dark, I've just put a new one in but if my air:fuel is fucked I should probably go grab a new one right?

Throw a new one in once you fix the problem. The plug isn't the problem.

If it's quite dark you're running rich. This could be the result of either poor fuel/air mixture in the carb or your ignition timing is off. Either could cause poor starting/running.

Since it's a used bike you just got I would start with ignition timing. You should do it regardless of your starting issue since you just got the bike and don't know its history (I think it's recommended to be done regularly on 2 stroke bikes). I've never done it on a 2 stroke bike, so I can't give any advice on it. I bet there's a ton of how-to guides online. You might need to find someone with a timing light to borrow.

If that isn't it then fuel/air mix is off. Again, look to how-to guides for your specific bike. You could try adjusting your mix first and maybe that solves the problem then you don't need to touch the timing, but you probably should do timing anyways so it's a logical start.

This,
Remove the carb, and completely dismantle it and clean it. Be very careful when taking it apart and take lots of pics so you can put it back together, a manual for rebuilding your carb would be very beneficial. It may seem a little daunting, but it's not too bad if you take your time.
Another thing that may help, replace the fuel lines and the carb boot (the rubber piece that goes between the motor and carb). If any air is getting in you will have problems.

Also, stop using starter fluid..... especially straight in the cylinder, I've blown a few two strokes up doing this.

RusticlesThis,
Remove the carb, and completely dismantle it and clean it. Be very careful when taking it apart and take lots of pics so you can put it back together, a manual for rebuilding your carb would be very beneficial. It may seem a little daunting, but it's not too bad if you take your time.
Another thing that may help, replace the fuel lines and the carb boot (the rubber piece that goes between the motor and carb). If any air is getting in you will have problems.

Also, stop using starter fluid..... especially straight in the cylinder, I've blown a few two strokes up doing this.

I cleaned the carb right away when I bought it + flushed and changed all fluids. Im thinking the new jets will help but idk at this point. Should I spray starter fluid on the air filter instead to get it started because I can can kick 100+ times and it'll hardly spudder. Starts up 1st or 2nd kick with starter fluid. Also gonna try messing with the FAR but don't wanna fuck it up worse.

That’ll work in the short term until you have time to have time to pull it apart. It shouldn’t give you to much trouble once it’s warm, and if it dosent kick just bump start it. Good luck bro -2001 CR250R

apttI cleaned the carb right away when I bought it + flushed and changed all fluids. Im thinking the new jets will help but idk at this point. Should I spray starter fluid on the air filter instead to get it started because I can can kick 100+ times and it'll hardly spudder. Starts up 1st or 2nd kick with starter fluid. Also gonna try messing with the FAR but don't wanna fuck it up worse.

It runs? Or runs well once started? How old is it?
Have you checked the reeds? It doesn’t really make sense that they are preventing starting, but easy enough to check.
From my experience and I’m no mechanic, but if a 2 stroke isn’t starting easy that means something is wrong. If you have to use starting fluid put it in the air filter, that might even give you some answers if fuel/air isn’t getting sucked in. Try a couple drops of mixed gas in the cylinder instead.

how well did you clean the carbs? This sounds like a choke/pilot jet issue. Those little bastards are hard to clean. If it runs fine after using the starter fluid then chances are that you don't need new jets, potentially you just have to clean yours. If it runs poorly at idle or has unusually high idle speeds then the pilot jet/air fuel mixture screw is the culprit. If the carbs are mikuni the air mixture screw is super sensitive and being 1/8 of a turn off can be a mess. get the service manual for your bike, they don't typically cost too much online and will have the carb specs for you. set the carb to the stock settings and adjust from there, so you have a baseline. also check the little things like choke cable, springs and for stuck chokes as those would cause the issue you are describing and are easy things to look at. could be timing as well but thats less likely as it starts easily and runs well with fluid. just remember the 2 stroke mantra---air, fuel and spark. one of them is not there when your bike won't start and for you i'd guess the issue is fuel related.

apttI cleaned the carb right away when I bought it + flushed and changed all fluids. Im thinking the new jets will help but idk at this point. Should I spray starter fluid on the air filter instead to get it started because I can can kick 100+ times and it'll hardly spudder. Starts up 1st or 2nd kick with starter fluid. Also gonna try messing with the FAR but don't wanna fuck it up worse.

Did you adjust your carburetor? Reduce the amount of fuel being delivered. Your not supposed to be using starter fluid all the time.
Jets could be the problem, but sometimes the spark arrestor, muffler or the air filter can be dirty but they would be obvious to see. Check your fuel filter and clean (or replace).

freestyler540Did you adjust your carburetor? Reduce the amount of fuel being delivered. Your not supposed to be using starter fluid all the time.
Jets could be the problem, but sometimes the spark arrestor, muffler or the air filter can be dirty but they would be obvious to see. Check your fuel filter and clean (or replace).

Update: I changed the main jet down and the pilot jet down, neither were clogged but it started 3rd kick cold after I did that. I also adjusted the air screw. Just need to make sure im not running too lean tonight and check the plug color.

apttUpdate: I changed the main jet down and the pilot jet down, neither were clogged but it started 3rd kick cold after I did that. I also adjusted the air screw. Just need to make sure im not running too lean tonight and check the plug color.

You dont need to open anything up to check combustion quality. As long as your engine doesnt hunt on idle (rpm constantly change), backfire or have a slow acceleration, the engine is well adjusted. For combustion quality, the exhaust color tells you everything to know.
Dark carbon smoke: Too much fuel or too little air is being delivered. This is an engine killer, as soot will damage everything from the liner to the muffler.
Blue Smoke: Too much oil mixture in the fuel. Its not the end of the world, but dilute the additive if you can.
Exhaust should be colorless, if you got that, the engine is running at its best and dont fuck with it until it starts acting weird.

If the engine has been left running for too long, a bio-film forms on surfaces. Its a gooey consistency and clogs small openings. They also impede the flow of the evaporated fuel and create turbulence in the ventury, giving bad fuel ratios.

freestyler540You dont need to open anything up to check combustion quality. As long as your engine doesnt hunt on idle (rpm constantly change), backfire or have a slow acceleration, the engine is well adjusted. For combustion quality, the exhaust color tells you everything to know.
Dark carbon smoke: Too much fuel or too little air is being delivered. This is an engine killer, as soot will damage everything from the liner to the muffler.
Blue Smoke: Too much oil mixture in the fuel. Its not the end of the world, but dilute the additive if you can.
Exhaust should be colorless, if you got that, the engine is running at its best and dont fuck with it until it starts acting weird.

If the engine has been left running for too long, a bio-film forms on surfaces. Its a gooey consistency and clogs small openings. They also impede the flow of the evaporated fuel and create turbulence in the ventury, giving bad fuel ratios.

So I went out tonight to test the combustion quality and it was good, somewhere around light tan and had pretty clear smoke but I still had a hell of a time starting it. Probably 30-40 kicks. Might have something to do with it being like 25 degrees in the garage. I hope that's all it is. Any other ideas to get it to start easier?

apttSo I went out tonight to test the combustion quality and it was good, somewhere around light tan and had pretty clear smoke but I still had a hell of a time starting it. Probably 30-40 kicks. Might have something to do with it being like 25 degrees in the garage. I hope that's all it is. Any other ideas to get it to start easier?

Yeah, cold makes it harder to start. But my chainsaw can start at that weather. Have you been using your choke? It helps prime the fuel. Maybe give more fuel on the idle.

Another thing to check is the fuel filter, and lines. Also check your fuel quality. I would of had so many headaches prevented if the fuel would of been mixed properly, or if someone would of just put stabiliser in the tank.

Another fuckin problem.... Now whenever I start it, which doesn't take starting fluid anymore, or whenever it's in neutral/ when I pull in the clutch it revs straight to redline and I can't get it to stop. The kill switch (which usually works) doesn't work at this point and the only way to turn it off is to pop it into a higher gear and stall it. It's a good thing I got this bike for a fucking steal kms

MLBThat’s your idle screw/ setting. The screw is too high so when you clutch, put it in neutral it’s just gonna rev to how high you set it.

It didn't used to do this though, and I never messed with the idle screw. It doesn't seem like the throttle cable is catching. My next idea is that it could be the slider catching. I have no idea at this point.

If I were you, I'd just pull the carb out completely and clean it. Pull off the bowl and make sure you get all the valves cleared. Sounds like it could use a good cleaning. Also search up how to tune your bike and how to set your carb up back to factory specs. Once the carb is at factory specs, go from there on tuning.

apttAnother fuckin problem.... Now whenever I start it, which doesn't take starting fluid anymore, or whenever it's in neutral/ when I pull in the clutch it revs straight to redline and I can't get it to stop. The kill switch (which usually works) doesn't work at this point and the only way to turn it off is to pop it into a higher gear and stall it. It's a good thing I got this bike for a fucking steal kms

Thats your throttle cable that must have slipped. Retention the cable or replace the spring on the carburetor throttle arm.
The killswitch cuts the fuel to the engine on some models or cuts the distributor's electrical source. Follow the switch's cable and it can solve a safety issue; Runnaway engines are deadly.

While you are at it, look at the kill switch. Either the valve is damaged or the things been hotwired.

So I figured out the idle problem... The boot in between the carb and cylinder wasnt snug enough... Causing it to run way lean. But now the carb is pouring gas out the bottom whenever I turn the gas on. It doesn't seem like the floats are sticking I took the carb apart 3 times to check floats. I tried the whole pressurized air up the drain trick with no luck. The floats seem good. The needle was a little off center but I fixed that with no avail. One problem after the next.

apttSo I figured out the idle problem... The boot in between the carb and cylinder wasnt snug enough... Causing it to run way lean. But now the carb is pouring gas out the bottom whenever I turn the gas on. It doesn't seem like the floats are sticking I took the carb apart 3 times to check floats. I tried the whole pressurized air up the drain trick with no luck. The floats seem good. The needle was a little off center but I fixed that with no avail. One problem after the next.

Could it be the oring around the needle valve is worn? Fuel maybe leaking through. A bent needle could be opening the valve at the wrong level. Can you replace the carburetor altogether? Could solve a lot of problems.

Look at it this way, you are learning a lot about 2 stroke engines on your own. I had to go to school for this.

freestyler540Could it be the oring around the needle valve is worn? Fuel maybe leaking through. A bent needle could be opening the valve at the wrong level. Can you replace the carburetor altogether? Could solve a lot of problems.

Look at it this way, you are learning a lot about 2 stroke engines on your own. I had to go to school for this.

I am definitely a hell of a lot faster getting a carb apart now haha. It's a 1989 yz250wr so new parts aren't terribly easy to find. There are a few on eBay but I bought this bike because it was a cheap bike, and a new carb would be 100$+ but I am willing to do that if it's last resort.

apttI am definitely a hell of a lot faster getting a carb apart now haha. It's a 1989 yz250wr so new parts aren't terribly easy to find. There are a few on eBay but I bought this bike because it was a cheap bike, and a new carb would be 100$+ but I am willing to do that if it's last resort.

Rebuilding small engines are a bitch. I never wanted to get myself into searching the internet for parts for hours and researching specs for compatibility.
Learnt my lesson with mountain bikes; I tried rebuilding my Kona Stinky 2004 for years, from scratch. 700$ in, I gave up and sold the fucker.

Check around small engine shops/ parts stores like NAPA even boat shops to weigh your options. You never know what these guys can have on hand. Some of these guys spend their lives having fun with older engines and have suppliers that can help.

freestyler540Rebuilding small engines are a bitch. I never wanted to get myself into searching the internet for parts for hours and researching specs for compatibility.
Learnt my lesson with mountain bikes; I tried rebuilding my Kona Stinky 2004 for years, from scratch. 700$ in, I gave up and sold the fucker.

Check around small engine shops/ parts stores like NAPA even boat shops to weigh your options. You never know what these guys can have on hand. Some of these guys spend their lives having fun with older engines and have suppliers that can help.

Well I gave in and bought a new carb and put it in last night. Bike started right up but now it's boggy at low RPMs and when in gear it has a cruise control of about 20mph. Im assuming that it's just tuning but I don't know what needs to be tuned haha.

apttWell I gave in and bought a new carb and put it in last night. Bike started right up but now it's boggy at low RPMs and when in gear it has a cruise control of about 20mph. Im assuming that it's just tuning but I don't know what needs to be tuned haha.

What do you mean by boggy? Does the engine seem to die until it revs to life at idle (hunting) or it doesn't develop power at low RPM?
Both cases are adjustments in the carburetor; which one depends on the situation. However, this is where my knowledge of carbs ends before entering details of the model.

So when its in gear, the bike takes off on you? Then it stops accelerating at 20mph? What is your engine speed at idle?Could be the engine runs too fast at idle. Decrease idle speed by checking the tachometer gauge and adjusting to the manufacturers speed. Did you run it off its wheels? if so, that normal. If not, sounds like the engine runs too fast at idle.

Try to find the users manual of your carburetor, it will show you where the adjustment screw is and how to tune it.

Apr 28 2018 7:22PM

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